1. Field of the Invention
The invention relates to an abnormality determination device and an abnormality determination method of a vehicle equipped with a stepped type automatic transmission. More particularly, the invention relates to a technology that performs abnormality determination regarding elements that are related to formation of a predetermined speed change step.
2. Description of the Related Art
In a vehicle equipped with a stepped type automatic transmission capable of forming a plurality of speed change steps, a known abnormality determination device determines whether or not the stepped type automatic transmission can normally form a speed change step.
For example, Japanese Patent Application Publication No. JP-A-2001-50382 describes a failure detection device in conjunction with a planetary gear type automatic transmission in which the switching among the speed change steps is performed by controlling the fastening (engagement) and release of a plurality of engagement devices. This failure detection device of the automatic transmission includes abnormality determination means for intentionally outputting a signal that causes the fastening of an engagement device that normally must not be fastened for a gear step, that is, an engagement device other than the engagement devices selected as a combination of devices to be fastened for the gear step, and for determining whether a fail-safe device that prevents interlock (simultaneous engagement) of the automatic transmission is reliably operating on the basis of whether or not pressure has been transmitted to the engagement device that normally must not be fastened.
Incidentally, in general, as for abnormalities due to valve sticking (valve fixation) of a fail-safe valve, a control valve, etc., or abnormalities of a detection switch that detects the pressure transmitted to engagement devices, etc., the abnormality determination needs to be performed in a state where a speed change step has actually been formed, or in a state where a command to form a speed change step has been output as shown in Japanese Patent Application Publication No. JP-A-2001-50382.
Then, in the case where there is an abnormality, such as the valve sticking or the like, which cannot be detected unless a speed change step has actually been formed, the shift to the speed change step having the abnormality may possibly be performed despite the abnormality thereof; thus, there is a possibility of deterioration of the drivability. Particularly, a high speed-side speed change step, which is less frequently used than a low speed-side speed change step, usually requires a relatively long time for the abnormality determination and the normality return determination, thus leading to a possibility of even greater deterioration of the drivability.